1. Field of the Present Invention
The present invention generally relates to the field of electronic systems and more particularly to an externally supplied circuit for rapidly precharging system nets.
2. History of Related Art
In the design of an electronic system, such as a circuit board populated with a plurality integrated circuit devices that are interconnected with a matrix of interconnects or "nets," it is desirable to precharge the net to a logical level such as the logical high level when the net is tri-stated. Precharging the net can improve system performance by reducing the time required for the net to transition from a high impedance state to a logical high state. If the tri-state voltage is close to or equal the logical high voltage, it will be appreciated that less time is required to transition the signal from the tri-state condition to the logical high condition. Preferably, the precharging circuitry is embedded in the drivers of the devices coupled to the net. Unfortunately, however, not all devices are designed and implemented with drivers incorporating adequate precharging circuitry. When such "non-conforming" devices are connected to a system net, problems in achieving a desired transition time may arise. More specifically, after a non-conforming device releases control of the net, the net may be in a partially or fully charged state such as a voltage intermediate between the logical high and logical low level. When the net is subsequently driven to a logical level, the amount of time required to transition the net may be in excess of the time permitted by the system timing constraints and the system may incorrectly interpret a logical level on the net. Compounding this problem are the significant difficulties and expense associated with attempting to rework or replace the non-conforming devices. Accordingly, it would be highly desirable to implement a solution that would enable adequate pre-charging of selected system nets without requiring modification of the existing devices.